The present invention relates to the production of memory modules, and more particularly to a method and apparatus for attaching integrated circuit chips to printed circuit boards.
There is an almost insatiable demand for additional semiconductor memory in personal computing applications. The usual practice is for systems manufacturers to ship personal computer systems with a minimum amount of memory installed and provide a way for the owners to add additional memory as their needs dictate. This protects the manufacturer from sometimes being on the wrong side of a price swing in the volatile semiconductor memory market and also lowers the price of the system being sold.
This practice creates a huge market for low cost, reliable memory modules that can be installed after the initial sale, either by users or other individuals that are not necessarily skilled in the art of computer hardware modification.
The physical need for this market has been met with memory modules such as the 88 pin Personal Computer Memory Card International Association (PCMCIA) card and a variety of Single In-line Memory Modules (known as SIMMs). These devices typically include a printed circuit board (PCB) and a number of discrete integrated circuit memory chips connected to the PCB in a manner that allows the PCB to be easily installed in a computer system.
One problem with the current technology is cost, since users are looking for the lowest cost solution to their memory storage needs. Current technology generally provides two methods of manufacturing memory modules. The most common method is to first package individual semiconductor chips into individual plastic packages, test each chip, and then attach the packages to a PCB, using a multi-step process. The multi-step process includes the steps of attaching the chips to a lead frame, connecting wires to the frame, injection molding the frame, plating the leads with tin, deflashing the molding compounds, bending the leads, testing the package, and so on. Obviously, this multi-step process is both cumbersome and expensive.
Another method for manufacturing memory modules is commonly referred to as "flip chip" technology, which utilizes solder balls to solder chips face-down on a substrate. Flip chips are typically used to create multichip memory modules. One disadvantage of conventional flip chips is that the thermal expansion/contraction properties of the materials used in the manufacturing process must be matched closely to prevent damage to the flip chips during use. Another disadvantage is that standard visual inspections cannot be performed on the flip chips, because the flip chips are attached face-down on the substrate, covering the connection with the substrate.